Data volumes communicated using mobile terminals are steadily increasing. Associated with the increased demand for mobile date exchange is a steady technical progress as defined, e.g., by the standards for the Global System for Mobile Communications (GSM), Universal Mobile Telecommunications Systems (UMTS) and Long Term Evolution (LTE), which improve data rates and user capacities. A result of the technical evolution is the coexistence of different generations of mobile communication standards. By way of example, a communication network may cover contiguous or overlapping areas by means of technically different Radio Access Technologies (RATs). In order to facilitate the mobility of the mobile device in the area covered by the communication network, the mobile terminal carries out cell search and other measurements (so-called “mobility measurements”), by which the terminal can move from cell to cell in a seamless fashion while, e.g., monitoring a paging channel or being engaged in a data transfer or voice call.
Therefore, it would be desirable for modern mobile terminals to comprise a multi-RAT modem that simultaneously supports up to three RATs. The situation is, however, complicated by measurement requirements, which have to be fulfilled for each of the supported RATs, and which may not only differ for each of the supported RATs, but may also depend on the RAT of a currently serving cell.
Existing mobile terminals typically contain only two so-called stacks for supporting, e.g., GSM and UMTS Terrestrial Radio Access (UTRA FDD), respectively. For two stacks it is possible to yield radio time for measuring on a carrier of the other currently non-serving RAT using a fixed scheduling on Discontinuous Reception (DRX) cycles or idle frames, e.g. in the GSM connected mode. However, as the number of supported RATs increases, the existing technique is no longer feasible. The existing methods of yielding radio time for mobility measurements require knowledge of the radio time needed by the other non-serving RAT. Hence, deriving such a fixed scheduling is becoming increasingly complicated due to the exponentially increasing combinatory complexity of the many schedules for each supported RAT. The complexity increases with the number of supported RATs, the number of monitored carriers for each RAT, a current DRX cycle length, etc.
In addition to the required mobility measurements for each supported RAT, there are further activities requiring radio time. Such activities include system information acquisition either in an idle mode, e.g. in an UTRA FDD Cell Paging Channel state or UTRA Registration Area Paging Channel state (URA-PCH state) having a shortest paging cycle of 80 ms, or in a connected mode using autonomous gaps that may overlap the measurements gaps, e.g. in a connected mode of evolved UMTS Terrestrial Radio Access (e-UTRAN connected mode). Another example of activities that may disturb, or be disturbed by, the conventional scheduling techniques includes a support for a dual Subscriber Identity Module (dual SIM support) or support for different network providers.
International application PCT/EP2011/054093 (published as WO 2011/113919) claiming the priority of applications EP 10 002 939.6 and U.S. 61/318,530 addresses a problem related to the fact that e-UTRA measurement gaps are short, which may affect the mobility measurement, and suggests scheduling measurements on the same e-UTRA carrier in consecutive or temporarily nearby measurement gaps. However, this technique does not take into account if the RAT requirement for, e.g., GSM includes reconfirming of a cell during the time of the consecutive measurement gaps. Potentially, the time occupied by the consecutive measurement gaps would have been the last opportunity to fulfil measurement performance requirements of GSM. Latter scenario primarily applies whenever GSM is not the currently serving RAT. Generally, failing to reconfirm a cell in the correct time period may entail formal and/or technical consequences. First, such a mobile device may fail a conformance test and may not be type approved. A Type Allocation Code (TAC), which is included as initial 8 digits of the 15-digit International Mobile Equipment Identity (IMEI) code, is however necessary to uniquely identify the mobile device. Second, the mobile device may have lost the GSM cell in the scenario without being aware thereof, which may have an impact on the mobility of the mobile device.
The conventional scheduling technique may, particularly in the presence of the other activities, harm certain carriers more than other carriers. At least under certain conditions, a more graceful degradation may be desirable, so that essentially all measured carriers experience a slight degradation rather than one or few carriers being subject to a severe degradation.